To most effectively develop any particular muscle group a resistive force should be applied to that muscle group which: (1) isolates, as much as is possible, the muscle group being developed while applying minimum components of force to other muscle groups. (2) is applied throughout the greatest possible range of contraction of the muscle group. (3) varies as a function of the positionally related strength capabilities of the muscle group as it actuates the body joint(s) being moved.
A major problem with present day "lat developing" machines, like the pulldown machine and the rowing machine, is that they do not isolate the arm adducting (latissimus dorsi or "lat") muscles of the back, which is due to the fact that they utilize a "pulling" movement which involves not only arm adduction but also concurrent arm flexion. "Pulling" movements, which involve flexion of the arms, bring the much weaker "arm flexing" biceps into the exercise movement and consequently limit the lat building potential of the exercise to the strength of the much weaker bicep muscles of the upper arms. The machine disclosed in this application, on the other hand, by fixing the position of the operator's shoulder joint and using a body-machine force-transmitting contact surface which applies a resistive force to the back side of the operator's upper arm through a circular path about the opeator's shoulder joint, eliminates the arm flexing component common to "pulling" movements leaving a pure arm adduction movement which isolates the arm adducting lat muscles so that their muscle building potential is no longer limited by the much weaker bicep muscles.
The arm adducting latissimus dorsi muscles of the back have their distal insertions in the humerus bone of the upper arm and their proximal insertions in the lumbar vertebrae and hip bone in the lower back region. This means that they cross not only the shoulder joint but also many spinal joints and therefore, upon contraction, not only adduct the arm but also curve the spine and rotate the hips upward toward the side contracting. This means that a greater range of contraction (and therefore muscle building potential) is available by not only rotating the arm about the shoulder joint but also concurrently rotating the hip and spine about some point of rotation which allows the lat muscles points of proximal insertion to move closer to their point of distal insertion throughout the exercise movement. The machine disclosed in this application takes advantage of the fact that the lat muscles cross more than one body joint, and obtains a greater range of muscle building contraction by exercising one side of the operator's body at a time, through the use of two rotating effort arms which apply resistive force to the operator's body at the back of the upper arm and the side of the hip on one side of the operator's body and an adjustable body-machine contact surface which fixes the position of the operator's rotating shoulder joint by applying a constraining force to the upper outside of the operator's non-rotating shoulder on the other side of the operator's body.
The few "lat developing" machines on the market which do apply a resistive force throughout a pure arm adduction movement are all of a bilateral design (both sides of the body being exercised concurrently), which does not allow the hip and spine to rotate toward the side contracting which, in turn, decreases the available range of contraction of the arm adducting lat muscles and consequently decreases the lat building potential of the exercise movement.
Due to joint mechanics, angles of pull of the lat muscles, and physiological make-up of the lat muscles, more force can be applied in the beginning through the middle of the arm adduction movement than toward the end of the movement, and the resistive force which the machine applies should vary in accordance. Most present day "lat developing" machines, like the pulldown machine or the rowing machine, apply a constant load which does not vary to correspond with the positionally related strength capabilities of the lat muscles being developed (this is the reason for the increased difficulty in a pulldown or rowing movement toward the end of the movement). The machine disclosed in this application, on the other hand, through the use of a 4-bar linkage/rotating weight arm force-varying mechanism which is mechanically linked to the two rotating effort arms on the machine, applies a resistive force which varies to correspond with the normal ability of the lat muscles to apply force throughout this body movement which, of course, results in greater lat building potential.
The few "lat developing" machines on the market which do apply a variably resistive force throughout a pure arm adduction movement, do it through the use of cams used in conjunction with cables or chains, all of which have inherent problems. The problem with cams is that they are relatively hard to manufacture. The problem with cables is that because of their relatively small cross sectional area, they carry very high stresses (a 1/8" cable carrying 200 lbs, for example, has a tensile stress in it of approximately 16,300 psi). These already high stresses are multiplied and become cyclic (introducing fatigue wear) when a cable moves along bending over a small diameter pulley. Because of the high tensile stresses involved, cables stretch (eventually decreasing the machine's intended range of motion) and eventually fray and wear out (leading to replacement or catastropic failure). Chains, while not suffering the fatigue wear that cables do, are subject to stretching at their many joints (which again decreases the machine's intended range of motion). They, also like cables, are subject to relatively high tensile stresses and in addition are noisy and introduce spurious drag to the machine. The force varying mechanism used on the machine disclosed in this application, on the other hand, consist of only three moving parts connected to each other and to the frame of the machine at a total of four pivotal joints, forming a 4-bar linkage. The three moving parts are all rigid members with relatively large cross sectional areas, which both eliminates the need to fabricate a relatively complex cam and eliminates the problem of deformation or failure of the moving parts due to excessive loads and fatigue (a disadvantage of cables and chains). Due to the fact that the force varying mechanism used on this machine has only four pivotal joints (and indeed, the whole machine has only seven pivotal joints), stretching at joints, noise, and spurious drag (disadvantages of chains) are all greatly reduced.
A body building machine must, of course, be practical, and in order for it to be practical it should be easily adjustable, in order to accomodate a wide range of operator sizes. The machine disclosed in this application covers a wide range of operator sizes with only two adjustments of body-machine contact surfaces. There are five body-machine contact surfaces on each side of this machine (both sides being symmetrical with each other). The first of these body-machine contact surfaces is fixed to an upper rotating effort arm and applies a resistive force to the back side of the operator's upper arm through a circular path about an axis which is common with the sagittal axis of rotation of the operator's rotating shoulder joint. This surface does not need to be adjustable because the distance between the operator's shoulder axis and the back of his upper arm does not vary significantly between operators. The second of these body-machine contact surfaces is attached to a second (lower) rotating effort arm and applies a resistive force to the side of the operator's hip on the contracting side of the body through a circular path about a sagittal axis which passes through approximately the center of the operator's back. This surface does not need to be adjustable relative to the centerline of the operator's body or the seat support surface because the distance between the side of the hip and the centerline of the body and the distance between the side of the hip and the operator's seat while sitting do not vary significantly between operators. The third of these is adjustably attached to the frame of the machine and applies a constraining force to the upper outside of the operator's non-rotating shoulder which serves the function of counteracting the components of force acting at the body-machine force-transmitting contact surfaces which engage the back of the operator's upper arm and the side of the operator's hip. This surface does have to be infinitely adjustable along a horizontal line which runs laterally across the operator's body because the distance between the operator's rotating shoulder joint and the outside of his opposite shoulder will vary both significantly and specifically between operators. The fourth of these is adjustably attached to the same (lower) rotating effort arm that the contact surface which engages the side of the operator's hip is attached to and applies a constraining force to the operator's seat while in the seated position which serves the function of supporting the operator's bodyweight while performing the exercise. This surface must also be infinitely adjustable approximately along a line running radially away from the lower effort arm's axis of rotation because the distance from the operator's rotating shoulder joint down along his spine to his seat while in the seated position will vary both significantly and specifically between operators. The fifth and final body-machine contact surface on each side of the machine is also fixed to the lower rotating effort arm and is positioned to engage the operator's upper back where it acts as a back support while performing the exercise. Infinite variability, which is required for the non-rotating shoulder engaging contact surface and the seat support surface which, in combination, allign the sagittal axis of rotation of the operator's rotating shoulder joint with the machine's upper effort arm's axis of rotation, is easily accomplished through the use of an engaging pair of internal and external threads which actuate a pair of telescoping tubes to which these body-machine contact surfaces are attached (same principle which a vise works on).
A second aspect of the practicality of a body building machine, beside its ability to accomodate a wide range of operator sizes, is the ease with which an operator can get in and out of it. The machine disclosed in this application is easy to get in and out of due to the fact that all of the body-machine forcetransmitting contact surfaces on the machine have open access parallel to the planes with which they make contact with the operator's body while performing the exercise as can be seen in the pictorial view of the machine in FIG. 1.